Electrodynamically operated circuit protective device



Feb. 2, 1965 R. M. PATRICK 3,168,626

ELECTRODYNAMICALLY OPERATED CIRCUIT PROTECTIVE DEVICE Filed Aug. 1, 1960 ELECTRICAL DEVICE 57 M E Q 5 RICHARD M. PATRICK INVENTOR.

ATTORNEYS United States Patent Ofilice 3,153,626 ELECTRGDYNAMECALLY OPERATED CIRCUIT PRQTECTIVE DEVICE Richard M. Patrick, Winchester, Mass, assignor to Avco Corporation, Cincinnati, Uhie, a corporatien of Delaware Filed 1, 196b, Ser. No. $6,644 9 Claims. (Cl. 2tltl87) The present invention relates to electrical safety devices and more particularly to high-voltage conductor fuses of the rapid action type which utilizes electrodynamic action of current supplied to the control device for removing it from the circuit.

The need for banks of high-voltage, high-capacity electrical devices is increasing rapidly and it is important that each device of the bank be fused so that failure of any one device does not destroy or seriously affect the remaining devices.

Circuit breakers which are exemplary of the prior art have heretofore been used to solve this type of problem. In the construction of such circuit breakers it is considered good design procedure to have the electrical circuit in the form of a U-shaped loop in which the incoming and outgoing current studs form the two sides and the movable contact is the bridging member of the U-shaped loop. With this design, difiiculties arise due to the excessively high magnetic forces which are exerted on the elements of the loop when the loop is subjected to short circuit current. The stationary incoming and outgoing current studs are designed as relatively heavy members securely anchored so as to successfully resist these forces. With respect to the moving contact or bridging member which has to move both from the open to the closed position and from the closed position to the open position in the presence of these forces, great difiiculty in securing proper operation has been experienced in the past.

To overcome these difiiculties it is common practice to provide additional and costly control mechanism. Obviously, such circuit breakers are costly, complex, of generally rugged construction and utilize a mechanical linkage which increases the time required for the circuit breaker to be actuated. But for the speed with which an individual device can be disconnected from the main lines, the de vice may explode and destroy adjacent equipment or endanger nearby personnel. Alternately an abnormal strain may be placed on the system thereby resulting in danger to life and other dangers that would inherently arise.

Accordingly, it is an object of the present invention to remedy these defects of the prior art.

Another object of the present invention is the provision of a novel high-voltage rapid action electrical safety device which is simple in structure and reliable in operation by providing two conductors insulated one from another and arranged and adapted to be in close and overlapping relation so that the current flows in opposite directions through them thereby rupturing one of the conductors under short circuit conditions.

A still further object of the present invention is the provision of two shimstock type conductors for highvoltage, high-capacitance applications wherein the conductors are arranged and adapted to be in close and overlapping relation one to another whereby the electrodynamic effects therefrom cause one of the conductors to be ruptured under short circuit conditions.

Another object of the present invention is the provision of thin, broad shim like metal conductors in spaced, overlapping, and insulated relation one to another connected in circuit with an electrical device to be protected to develop a mutual repulsion which results in rupture of at least one of the conductors under short circuit conditions and removes the electrical device from the circuit.

According to one feature of the present invention, shim- 3,168,526 l e-iterated Feb. 2, 1965 stock having a minimum thickness and a width sufficient to carry rated current is connected in series with each terminal of the electric device to be protected. The shimstock conductors are arranged in parallel and overlapping relationship one with another so that current in these conductors flows in opposite directions. The shimstock conductors are maintained in the aforementioned close relationship so that a mutual repulsion in the conductors is present in the overlapped region when current is flowing in the shimstock conductors. In a high-voltage, high-capacitance system a short circuit condition or the equivalent thereof in the device to be protected results in a repulsion between the shimstock conductors sutlicient to rupture at least one of them at its connections or therebetween and thereby open the circuit. The shimstock conductors serve not only as electrical conductors but also as fast acting fuses. By reason of their low mass and the large forces acting on them, opening or" the circuit is very rapid. As used herein the term rupture connotes a physical tearing or breaking as distinguished from melting.

These and other features, objects and advantages of the present invention will appear from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments of an electrical safety device in accordance with the present invention, and wherein:

FIGURE 1 is a pictorial view showing the invention in connection with an electrical device such as a capacitor wherein the metal container forms part of the electrical circuit;

FIGURE 2 is a diagrammatic representation showing the conductors connected in series with each other and one terminal of an electrical device; and

FIGURE 3 is a diagrammatic representation showing each conductor connected in series with a different terminal of an electrical device.

With reference to FIGURE 1, there is shown an electrical device it such as, for example, an electrolytic capacitor having a pair of binding posts 12-13. Binding post 12 is insulated from the metal container 1 of which the top wall 15 forms a part. The metal container 14, including top wall 15, is provided with a substantial thickness 16 to provide an electrically conductive, rigid, and strong container as is customary with electrolytic capacitors. Binding post is electrically connected to the top wall 15. In a conventional application the electrical circuit f r such a device includes the binding posts, the electrolyte, and the metal container. As shown in FIG- URE 1, this electrical circuit additionally includes a thin broad shim-like conductor 17 electrically connected to and supported at one end by binding post 12 and electrically connected to and supported at its other end by a bus bar 18 which is insulated from the top wall 15 by suitable insulating material 19. By way of example, conductor 17 may befixedly attached to the bus bar 18 at its said other end as by soldering and provided with a passage at its said one end whereby it may be fixedly attached by means of nut 21 to binding post 12, and thereby maintained in substantially fixed and close proximty to top wall 15. If desired the insulating material 19 may extend the length of conductor 17. A potential such as 20,000 volts DC. may be applied across binding post 13 and bus bar 18 from a suitable source (not shown) by conventional con ductors or buses 22-23. As may now be apparent, conductor 17, which may be of the order of .004 inch thick and of suficient width to carry rated current, is maintained in predetermined space, insulated, and overlapping relationship with the top wall 15 and is electrically connected in series therewith. Current flow through the electrical device ll must of necessity flow through conductor 17 and top wall 15. Additionally, the current flowing in conductor 17 and top wall 15 flows in opposite directions and, because conductor 1'? and top wall are in overlapping relationship, develops a mutual repulsion there between because of well-known electrodynamic effects.

By reason of the tenuous character of conductor 17 due to its shim-like configuration and the substantial strength of top wall 15 due to its thickness 16 which is many times that of conductor 17, it will be readily apparent that upon the application of physical stress to eit er of these elements, conductor 1'7 w l fail completely before the top wall T15 begins to approach its failing point. However, so long as physical stress is not applied to conductor 1'7, normal operation of device 11 will be obtained since the width and composition of conductor 17 is selected to pass rated current.

If now it is assumed that device it develops an internal short, a large surge of current will flow through conductor 17, the shorted device 11, and through conductors 2243. The current flowing in conductor 17 and top wall 15 flows in opposite directions, and, because of the close proximity and overlapping arrangement of these conductors, develops a mutual repulsion of electrodynat .ic force between them, which tends to force them in opposite directions. It is this mutual repulsion during short circuit conditions that causes conductor 17 to be ruptured and open the circuit. in a high voltage, high capacitance, system, the repulsion is violent and actually rips the shim-like conductor from its bus bar and/ or its point of connection with the device to be protected. Thus, the shim-like conductor serves as a conductor during normal operating conditions and also as a fast-acting fuse du -ig short circuit or abnormal conditions. Because of its low mass and the large forces acting on conductor 17, opening of the circuit is very rapid. in a capacitor bank, which may have any number of different capacitors connected in parallel, use of the present invention assures safety for the entire bank. But for the speed with which an individual capacitor can be disconnected when it internally shorts, the capacitor might explode, thereby destroying the entire bank.

Those skilled in the art will readily appreciate that the bus bars and the like necessarily must be heavily constructed so that the forces that rupture the shim-like conductor do not also destroy the bus bars and their connections to the other capacitors. Those skilled in the art will also readily appreciate that if the use of the metal case of an electrical device is unattractive for example, because of structural configurations, a portion of a bus bar or the like equivalent to top wall 15 both in construction and function may be substituted therefor. Conductor 17 must, of course, be in the described relationship with the conductor substituted for top wall 15.

PEGURE 2 diagrammatically illustrates the invention for applications where the electrical device to be protected is a two-terminal device of the type where a metal case or the like cannot be utilized in the manner shown and described in connection with FIGURE 1. Shown in ilGURE 2 is an electrical device 31 having a pair of binding posts 32 and 355. Binding post 32 is connected to one side of a source of current (not shown) and binding post 33 is connected to one end of a heavily constructed bus bar Fixedly connected as by soldering, to the other end of bus bar 3 is a tenuous shim-like conductor 35 capable of carrying the rated current of the electrical device 31. A second shim-like conductor as substantially identical to conductor 35 is connected as by soldering to a bus bar 3? substantially identical to bus bar 34-. Bus bar 37 is connected to the other side of the aforementioned source of current. Interposed between and fixedly connected to the remaining ends of conductors 3536 is a heavily reinforced conductive member 33. Member 38 is attached to a suitable support 39 by means of bolt ll and is insulated therefrom by suitable insulating members 42 and 33. As may now be apparent, the tenuous conductors 35-36, while electrically connected in series, are maintained in spaced, in-

,ieaea sulated, and overlapping r tionship one with another and the same current required by the device 31 fiows in opposite directions through conductors 35416, indicated by arrows 44-45, and develops a mutual repulsion, indicated by arrows 46 17, which tends to physically force the middle portions of conductors 3536 apart since their end portions are fixedly held by bus bars 3 5-37, and the conductive member Upon development of a short circuit condition or the equivalent thereof in device 31, the mutual repulsion developed by the increase of current flow in excess of a predetermined amount such as, for example, rated current, exerts sufficient physical force on conductors 35-36 to rip one or both of these conductors from their connections to the bus bars 34-37 or conductive member 38 and open the circuit.

The invention is shown diagrammatically in PEGURES 2 and 3 on a greatly enlarged scale to facilitate understanding of the invention. It is to be understood that the shim-like conductors may be held in the desired fixed and overlapping position by any suitable means diiferent from that shown and described herein by way of exampie. The shim-like conductors may also be insulated one from another by interposing a relatively thin sheet of suitable insulation between them, thus providing minimum spacing. Further, the conductors may be provided with configurations different from that shown and described herein by way of example, so long as the conductors are arranged and connected in circuit with the device to be protected to develop the required mutual repulsion and the configuration selected is such as to cause at least one of the conductors to rupture when the current, and hence, the mutual repulsion, exceeds a predetermined amount. Also, as was pointed out in connection with FlGURE 1, only one shim-like conductor may be used if desired.

FIGURE 3 shows diagrammatically an alternate arrangement wherein each conductor 51-52, for example, of shirnstock configuration is separately connected to a different bus bar 53-54 and a diiferent binding post 55-55 of the electrical device 57. Arrows 58-59 indicate current flow and arrows 6162 indicate the mutual repulsion. Comparison of FIGURES 2 and 3 will readily show that the current flow, the development of the mutual repulsion, spacing, etc, as shown in FIGURE 3, is the full equivalent of that shown and described in FIGURE 1 or 2.

Although the present invention may be used in the protection of a wide number of electrical devices, it finds greatest utility in applications where the duty cycle of the device'to be protected is relatively short, i.e., in high voltage, high frequency, and high capacitance systems.

The use of shim-like conductors as a conductor-fuse having a minimum thickness and substantial width is particularly advantageous in high frequency applications. in the foregoing, the present invention has been described solely in connection with specific illustrative embodiments thereof. It is to be understood that the same are susceptible of Various modifications within the spirit and scope of the present invention and it is intended to cover all such changes and modifications except as limited by the appended claims.

What is claimed is:

1. In combination with an electrical device to be protected the combination comprising: current conducting means having a substantially fiat surface forming a part of the electrical circuit for supplying current to said electrical device; a substantially lat electrically conducting member in insulated and overlapping relationship with said current conducting means, means serially connected therewith to establish current flow in opposite directions through said member and said current conducting means to develop a mutual repulsion therebetween; and means for fixedly maintaining the ends of said electrically conducting member in said insulated and overlapping relationship with said current-conducting means, said electrically conducting member having a cross section to cause it to rupture before heating sufiicient to weaken said electrically conducting member occurs when said mutual repulsion exceeds a predetermined amount.

2. In combination with an electrical device to be protected the combination comprising: current conducting means having a substantially flat surface forming a part of the electricalcircuit for supplying current to said electrical device; a substantially fiat electrically conducting member in insulated and overlapping relationship with the flat surface of said current conducting means, means serially connected therewith to establish current flow in opposite directions through said member and said current conducting means to develop a mutual repulsion therebetween; and means for maintaining each of two spaced apart points on said conducting member in a fixed position, said electrically conducting member being structurally weaker than said conducting means and having a cross section to cause it to rupture before heating sufllcient to weaken said electrically-conducting member occurs when said mutual repulsion exceeds a predetermined amount.

3. In an electrical circuit the combination comprising: a pair of fiat and substantially parallel conductors in spaced and overlapping relationship one with another, means serially connected to said conductors to establish substantially the same current flow through them in 0pp0- site directions to develop a mutual repulsion; and means for fixedly maintaining the ends of said pair of conductors in said spaced and overlapping relationship, at least one of said conductors having a low mass and a thickness substantially less than its width to cause said one of said conductors to rupture before heating sulficient to weaken said at least one of said conductors occurs when said mutual repulsion exceeds a predetermined amount.

4. In an electrical circuit the combination comprising: an electrical device; a pair of flat and substantially parallel conductors in spaced and overlapping relationship one with another connected in series with said electrical device, means serially connected to said conductors to establish substantially the same current flow through them in opposite directions to develop a mutual repulsion; and

cans for fixedly maintaining the ends of said pair of conductors in said spaced and overlapping relationship, at least one of said conductors having a low mass and a thickness substantially less than its width to cause said one of said conductors to rupture before heating sufiicient to weaken said at least one of said conductors occurs when said mutual repulsion exceeds a predetermined amount.

5. In an electrical circuit the combination comprising: an electrical device; means to supply current to said electrical device; a pair of flat and substantially parallel conductors in spaced and overlapping relationship one with another connected in series with said electrical device and said means to supply current to said electrical device to establish current flow through said electrical device and through said conductors in opposite directions to develop a mutual repulsion; and means for fixedly maintaining the ends of said conductors in said spaced and overlapping relationship, at least one of said conductors having a low mass and a thickness substantially less than its width to cause said one of said conductors to rupture before t3 heating sufiicient to weaken said at least one of said conductors occurs when said mutual repulsion exceeds a predetermined amount.

6. In a high-voltage electrical circuit the combination comprising: an electrical device; means to supply current to said electrical device; a pair of flat and substantially parallel conductors in predetermined spaced and overlapping relationship one with another connected in series with said electrical device to establish current flow through said electrical device and through said conductors in opposite directions to develop a mutual repulsion between said conductors; and means for fixedly maintaining the ends of said pair of conductors in said spaced and overlapping relationship, at least one of said conductors having a low mass and a thickness substantially less than its width, said thickness and width providing a cross section and said conductors being spaced and overlapped one with another whereby said mutual repulsion causes said at least one of said conductors to rupture before heating sufiicient to weaken said at least one of said conductors occurs when current flowing through said at least one of said conductors exceeds a predetermined amount.

7. In a high-voltage circuit breaker for protecting an electrical device the combination comprising: first and second conductors of shimstock configuration; means for maintaining said conductors in spaced, overlapping and insulated relationship one with another; means for fixedly maintaining the ends of said first and second conductors in said spaced and overlapping relationship; and means for connecting said conductors and said electrical device in series to establish current flow through said electrical evice and through said conductors in opposite directions for exerting an electrodynamic force between said conductors tending to displace said conductors, said conductors having a cross section and being spaced and overlapped one with another to cause said electrodynamic force to rupture at least one of said conductors before heating sutiicient to weaken said conductors occurs when current flowing through said conductors exceeds a predetermined amount.

8. The combination as defined in claim 7 wherein said means for connecting said conductors and said electrical device in series comprises means for separately connecting one end of each conductor to said electrical device.

9. The combination as defined in claim 7 wherein said means for connecting said conductors and said electrical device in series comprises means for connecting one end of said first conductor to a corresponding end of said second conductor, and means for connecting the other end of said second conductor to said electrical device.

References Cited in the file of this patent UNITED STATES PATENTS 999,780 Harris Aug. 8, 1911 1,635,544 Crichton July 12, 1927 1,728,020 Traver Sept. 10, 1929 2,734,110 Jacobs Feb. 7, 1956 2,794,097 Jacobs May 28, 1957 2,922,928 Raudabaugh Jan. 26, 1960 3,002,065 Latour Sept. 26, 1961 3,068,379 Cole Dec. 11, 1962 

1. IN COMBINATION WITH AN ELECTRICAL DEVICE TO BE PROTECTED THE COMBINATION COMPRISING: CURRENT CONDUCTING MEANS HAVING A SUBSTANTIALLY FLAT SURFACE FORMING A PART OF THE ELECTRICAL CIRCUIT FOR SUPPLYING CURRENT TO SAID ELECTRICAL DEVICE; A SUBSTANTIALLY FLAT ELECTRICALLY CONDUCTING MEMBER IN INSULATED AND OVERLAPPING RELATIONSHIP WITH SAID CURRENT CONDUCTING MEANS, MEANS SERIALLY CONNECTED THEREWITH TO ESTABLISH CURRENT FLOW IN OPPOSITE DIRECTIONS THROUGH SAID MEMBER AND SAID CURRENT CONDUCTING MEANS TO DEVELOP A MUTUAL REPULSION THEREBETWEEN; AND MEANS FOR FIXEDLY MAINTAINING THE ENDS OF SAID ELECTRICALLY CONDUCTING MEMBER IN SAID INSULATED AND OVERLAPPING RELATIONSHIP WITH SAID CURRENT-CONDUCTING MEANS, SAID ELECTRICALLY CONDUCTING MEMBER HAVING A CROSS SECTION TO CAUSE IT TO RUPTURE BEFORE HEATING SUFFICIENT TO WEAKEN SAID ELECTRICALLY CONDUCTING MEMBER OCCURS WHEN SAID MUTUAL REPULSION EXCEEDS A PREDETERMINED AMOUNT. 